Method and device for transporting an object at variable speed

ABSTRACT

A device and a method for transporting a flat object are provided. A feeder module temporarily holds the object in a feeder gripping area and transports it. A first transfer component takes the object over from the feeder module, holds it temporarily in a first transfer gripping area, transports it in the first transfer gripping area at a first transfer speed which can be changed in terms of time and passes it on to the second transfer component. A second transfer component takes the object over from the first transfer component, holds it temporarily in a second transfer gripping area, transports it in the second transfer gripping area at a second transfer speed which can be changed in terms of time and passes it on to a removal module. The removal module temporarily holds the object in a removal gripping area and transports it.

The invention relates to a device and a method for transporting a flat object, in particular an item of mail, in a specified transport direction.

A device with the features stated in the preamble of claim 1 and a method with the features stated in the preamble of claim 9 are known from DE 19753419 C1. The device described there transports objects in the form of flat items of mail. The transfer module described there comprises two conveyors positioned opposite each other which together transport the items of mail, taking them over from a feeder module and passing them on to a removal module.

The object underlying the invention is to provide a device with the features stated in the preamble of claim 1 and a method with the features stated in claim 9, whereby the transfer module applies lower accelerations to the object without compressing or pulling it.

The object is achieved by a device with the features stated in claim 1 and a method with the features stated in claim 9. Advantageous configurations are stated in the subordinate claims.

In accordance with the invention the transfer module is divided into two transfer components. These two transfer components are controllable independently of each other and in each case exhibit a drive unit and a gripping area.

An object passing through the device in transport direction is first temporarily held and transported by the feeder module, then temporarily held and transported by the first transfer component, then temporarily held and transported by the second transfer component and finally temporarily held and transported by the removal module.

The first transfer component takes the object over from the feeder gripping area and holds it temporarily in the first transfer gripping area. Because the distance from the feeder gripping area to the second transfer gripping area is greater than the length of the object in transport direction, the object is held for a certain period of time only by the first transfer gripping area and during this period of time is neither held in the feeder gripping area nor in the second transfer gripping area. This period of time is between the timepoint at which the object leaves the feeder gripping area and the timepoint at which the object reaches the second transfer gripping area. During this period of time the first transfer component is able to change the transport speed of the object without the object being held and as a result pulled or compressed by a gripping area on another part of the device.

Next the second transfer component takes the object over from the first transfer component and holds it temporarily in the second transfer gripping area. Because the distance from the first transfer gripping area to the removal gripping area is greater than the length of the object in transport direction the object is held for a certain period of time only by the second transfer gripping area. This period of time is between the timepoint at which the object leaves the first transfer gripping area and the timepoint at which the object reaches the removal gripping area. During this period of time the second transfer component is able to change the transport speed of the object without the object being held and as a result pulled or compressed by a gripping area on another part of the device.

Next the second transfer component passes the object on to the removal module with the removal gripping area.

One advantage of the invention is the following: To achieve the same difference between the feed and removal speed the device in accordance with the invention applies a lower acceleration or delay to the object than known devices. This is brought about in particular by the presence of two separate transfer components which change the feed speed to the removal speed in two stages. The lower acceleration is particularly advantageous if the object is sensitive and could be damaged by excessive acceleration.

Preferably the distance from the first transfer gripping area to the second transfer gripping area is smaller than the length of the object. This has the effect that the object is always held by one gripping area as it is being transported by the transfer module.

A further preferred configuration provides that the device is configured in such a way that between the feeder gripping area (Z-K) and the first transfer gripping area (K1) the object travels a distance which is smaller than the length of the object in transport direction (T). The distance which the object travels between the second transfer gripping area (K2) and the removal gripping area (W-K) is also smaller than the length of the object in transport direction (T). This has the effect that the object is always held by one gripping area while it is being transported into and out of the transfer module.

The invention is described below with reference to an exemplary embodiment, in which;

FIG. 1 shows the device with a feeder module, a first and a second transfer component and a removal module.

In the exemplary embodiment the device in accordance with the invention is used to transport flat items of mail. The device is installed in a sorting machine for sorting items of mail. The items of mail pass through various subsystems of the sorting machine in a stream of consecutive mail items.

So that these subsystems function reliably there has to be a minimum gap between two consecutive mail items in the stream. This minimum gap is defined as the lower limit for the distance between the rear edge of the item of mail in front and the front edge of the following item of mail. To ensure that the throughput through the sorting machine is and remains adequately high, however, the distance between two consecutive items of mail must not be greater than the specified upper limit.

As items of mail pass through the sorting machine the gap between two consecutive items of mail may be too big or too small. To correct this incorrect distance automatically the sorting machine exhibits at least one gap correction module which the stream of mail passes through. In the exemplary embodiment the device in accordance with the invention functions as this gap correction module.

Before two consecutive items of mail pass through the transfer module of the gap correction module the distance between them is measured. Preferably a light barrier measures this distance. Its beam of light is interrupted by the items of mail. The time span in which the beam of light is not interrupted is measured. The feed speed at which the items of mail pass through the feeder module is known. From this feed speed and the measured time span the distance is calculated.

If the distance is too great the following item of mail is temporarily accelerated relatively to the item of mail in front, which reduces the distance. If, on the other hand, the distance is too small the following item of mail is temporarily delayed, i.e. transported more slowly, which increases the distance.

The feeder module, the two transfer components and the removal module in each case comprise at least two endless conveyor belts which in each case run round several rollers and are tensioned to an adequate level of tightness. In each case two conveyor belts positioned opposite each other exert a frictional force on an item of mail that is between them. This enables the two conveyor belts to transport the item of mail without any slip.

FIG. 1 shows a plan view of the device with a feeder module, a first and a second transfer component and a removal module.

In the example shown in FIG. 1 the feeder module comprises

-   -   two driven belt pulleys, whereby the driven belt pulley 1 is         shown in FIG. 1 and the other driven belt pulley is not,     -   several non-driven belt pulleys, whereby the non-driven belt         pulley 2 is shown in FIG. 1,     -   two driven endless conveyor belts F1-Z and F2-Z, whereby the         endless conveyor belt F1-Z and the belt pulley 1 and further         belt pulleys and the endless conveyor belt F2-Z run round the         belt pulley 2 and further belt pulleys.

The first transfer component Ü1 comprises

-   -   two driven belt pulleys 4, 11     -   four non-driven belt pulleys 3, 5, 9, 10,     -   two driven endless conveyor belts F1-Ü1 and F2-Ü1, and     -   a first drive unit, not shown, for turning the two belt pulleys         4, 11 at the same speed.

The endless conveyor belt F1-Ü1 runs round the three belt pulleys 3, 4 and 5. The endless conveyor belt F2-Ü1 runs round the three belt conveyors 9, 10 and 11.

The second transfer component Ü2 comprises

-   -   a second drive unit, not shown, for turning the two belt pulleys         8, 12 at the same speed,     -   two driven belt pulleys 8, 12     -   five non-driven belt pulleys 6, 7, 12, 14, 15, 17,     -   two idler pulleys 13, 16 and     -   two driven endless conveyor belts F1-Ü2 and F2-Ü2.

The endless conveyor belt F1-Ü2 runs round the three belt pulleys 6, 7 and 8. The endless conveyor belt F2-Ü2 runs round the four belt pulleys 12, 14, 15 and 17. The two idler pulleys 13, 16 tighten the endless conveyor belt F2-Ü2.

In an alternative configuration only the two conveyor belts F1-Ü1 and F1-Ü2 are driven. The two other conveyor belts F2-Ü1 and F2-Ü2 are also turned when the driven conveyor belts F1-Ü1 and F1-Ü2 turn.

In upright position an item of mail is held and transported by in each case two endless conveyor belts positioned opposite each other, with a longitudinal edge of the mail item pointing downwards and a lateral edge pointing forwards in transport direction.

In the exemplary embodiment the conveyor belts exert an influence on the items of mail by means of a friction contact. As a result, four gripping areas Z-K, K1, K2 and W-K are created between in each case two conveyor belts positioned opposite each other.

The feeder gripping zone Z-K of the feeder module is formed by the conveyor belts F1-Z and F2-Z and ends—seen in transport direction Z—in roller 1—more precisely: in a vertical on the parallel conveyor belts F2-Z and F1-Z through the middle point of roller 1. The first transfer gripping area K1 is formed by the conveyor belts F1-Ü1 and F1-Ü2 and is limited by the two rollers 3 and 4 and belongs to the first transfer component. The second transfer gripping zone K2 is formed by the conveyor belts F2-Ü1 and F2-Ü2 and is limited by the two rollers 12 and 17 and belongs to the second transfer component. The removal gripping area W-K of the removal module is formed by the conveyor belts F1-W and F2-W and begins in roller 17.

In the example of FIG. 1 the items of mail are transported from top to bottom in transport direction T. The lengths of the mail items—seen in transport direction—vary. The following are, however, given:

-   -   a minimum length L_min, i.e. a lower limit, and     -   a maximum length L_max, i.e. an upper limit         for the length of each item of mail transported. The length of         each mail item is therefore between L_min and L_max.

Preferably, items of mail which are shorter than L_min or longer than L_max are sorted out in advance and not transported through the sorting machine, because they are not suitable for machine-processing.

The gap correction module is designed in such a way that each item of mail is always held by at least one gripping area. This is made possible by

-   -   the distance which an item of mail travels from roller 1 (end of         the feeder gripping area Z-K) to roller 3 (start of the first         transfer gripping area K1),     -   the distance which an item of mail travels from roller 4 (end of         the first transfer gripping area K1) to roller 17 (start of the         second transfer gripping area K2) and     -   the distance which an item of mail travels from roller 12 (end         of the second transfer gripping area K2) to roller 17 (start of         the removal gripping area W-K)         being in each case smaller than L_min. After L_min has been         specified the rollers are arranged accordingly. By arranging the         rollers differently the device can be adapted to different         values for L_min or L_max.

The item of mail should not be compressed during transport. A compression would occur if the item of mail were held simultaneously by two conveyor belts turning at different speeds. A suitable control therefore ensures the following:

-   -   For as long as an item of mail is held both in the feeder         gripping area Z-K as well as in the first transfer gripping area         K1 the conveyor belts F1-Z and F2-Z of the feeder module and the         conveyor belts F1-Ü1 and F2-Ü1 of the first transfer component         are all turned at the same speed.     -   For as long as an item of mail is held both in the first         transfer gripping area K1 as well as in the second transfer         griping area K2 the conveyor belts F1-Ü1 and F2-Ü1 of the first         transfer component and the conveyor belts F1-Ü2 and F2-Ü2 of the         second transfer component are all turned at the same speed.     -   For as long as an item of mail is held both in the second         transfer gripping area K2 as well as in the removal gripping         area K2 the conveyor belts F1-Ü2 and F2-Ü2 of the second         transfer component Ü2 and the conveyor belts F1-W and F2-W of         the removal module are all turned at the same speed.

In the exemplary embodiment the conveyor belts F1-Z, F2-Z, F1-W and F2-W turn at a constant speed in terms of time. It is possible for the four conveyor belts to turn at the same time. It is also possible for the two conveyor belts F1-Z and F2-Z to turn at a feed speed and the two conveyor belts F1-W and F2-W to turn at a removal speed, whereby the feed and removal speed differ.

The speed of the conveyor belts F1-Ü1 and F2-Ü1 of the first transfer component Ü1 can be set and changed independently of the speeds of all the other conveyor belts after the rear edge of the item of mail has left the feeder gripping area Z-K and before the front edge of this item of mail has reached the second transfer gripping area K2. In this period of time the item of mail is exclusively held by the first transfer gripping area K1 and can be accelerated or delayed without being pulled or compressed.

Correspondingly, the speed of conveyor belts F1-Ü2 and F2-Ü2 of the second transfer component Ü2 can be set and changed independently of the speeds of all the other conveyor belts after the rear edge of the item of mail has left the first transfer gripping area K1 and before the front edge of this item of mail has reached the removal gripping area W-K. In this period of time the item of mail is held exclusively by the second transfer gripping area K2.

This control uses as entry variable the position at which an item of mail to be transported finds itself precisely at the time. The device therefore preferably incorporates at least one light barrier Li. This light barrier Li includes a transmitter 20 and a receiver 21. It is arranged at the end of the feeder gripping area Z-K or directly behind it. An item of mail which leaves the feeder gripping area interrupts the beam of light LS emitted by the transmitter 20. This is registered by the receiver 21. Because the speeds at which the transfer components Ü1, Ü2 and the removal module W-K transport the item of mail are known from the control of the drives it can be automatically calculated when the item of mail reaches which gripping area and when it leaves that area.

LIST OF REFERENCE CHARACTERS

Reference characters Meaning  1 driven belt pulley of F1-Z  2 non-driven belt pulley of F1-Z  3, 5 non-driven belt pulleys of F1-Ü1  4 driven belt pulley of F1-Ü1  6, 7 non-driven belt pulleys of F1-Ü2  8 driven belt pulley of F1-Ü2  9, 10 non-driven belt pulleys of F2-Ü1 11 driven belt pulley of F2-Ü1 12 driven belt pulley of F2-Ü2 14, 15, 17 non-driven belt pulleys of F2-Ü2 13, 16 non-driven idler pulleys of F2-Ü2 18 non-driven belt pulleys of F1-W 19 non-driven belt pulleys of F2-W 20 transmitter of the light barrier Li 21 receiver of the light barrier Li F1-Ü1, F2-Ü1 endless conveyor belts of the first transfer component Ü1 F1-Ü2, F2-Ü2 endless conveyor belts of the second transfer component Ü2 F1-W, F2-W endless conveyor belts of the removal module W F1-Z, F2-Z endless conveyor belts of the feeder module Z K1 first transfer gripping area K2 second transfer gripping area Li light barrier L_min minimum length of an item of mail L_max maximum length of an item of mail LS light beam of the light barrier Li T transport direction Ü1 first transfer component Ü2 second transfer component W removal module W-K removal gripping area Z feeder module Z-K feeder gripping area 

1.-11. (canceled)
 12. A device for the transport of a flat object in a transport direction, comprising: a feeder module with a feeder gripping area, the feeder module holds and transports the object in the feeder gripping area; a removal module with a removal gripping area, the removal module holds and transports the object in the removal gripping area; and a transfer module comprising: a first transfer component that includes a first drive unit and a first transfer gripping area, and a second transfer component that includes a second drive unit and a second transfer gripping area, wherein the first transfer component receives the object from the feeder module, the first transfer component holds the received object in the first transfer gripping area and transports the received object via a first drive to the second transfer component, wherein the second transfer component receives the object from the first transfer component, the second transfer component holds the received object in the second transfer gripping area and transports the received object via a second drive to the removal module, wherein the distance the object travels between the first transfer gripping area and the removal gripping area is greater than the length of the object in transport direction, and wherein the distance the object travels between the transfer gripping area and the second transfer gripping area is greater than the length of the object in transport direction.
 13. The device as claimed in claim 12, wherein the distance the object travels between the first transfer gripping area and the second transfer gripping area is smaller than the length of the object in transport direction.
 14. The device as claimed in claim 12, wherein the distance the object travels between the feeder gripping area and the first transfer gripping area is smaller than the length of the object in transport direction, and wherein the distance the object travels between the second transfer gripping area and the removal gripping area is smaller than the length of the object in transport direction.
 15. The device as claimed in claim 12, wherein a change of a first speed produced by the first drive is independent of a change of a second speed produced by the second drive.
 16. The device as claimed in claim 12, further comprising a controller for controlling the first drive and the second drive, such that: the first transfer component transports the object at the same speed as the feeder module when the object is held both in the feeder gripping area and in the first transfer gripping area, and the second transfer component transports the object at the same speed as the removal module when the object is held both in the second transfer gripping area and in the removal gripping area.
 17. The device as claimed in claim 12, wherein at least one of the two transfer components includes: a first driven endless conveyor belt that runs round at least two rollers, and a second endless conveyor belt that runs round at least two further rollers, wherein the first and second endless conveyor belts are arranged such that the transfer gripping area of the respective transfer component is between the two endless conveyor belts and is limited by two of the rollers.
 18. A sorting machine for sorting flat items of mail, comprising: a transport device, comprising: a feeder module with a feeder gripping area, the feeder module holds and transports the object in the feeder gripping area, and a removal module with a removal gripping area, the removal module holds and transports the object in the removal gripping area a transfer module comprising: a first transfer component that includes a first drive unit and a first transfer gripping area, and a second transfer component that includes a second drive unit and a second transfer gripping area, wherein the first transfer component receives the object from the feeder module, the first transfer component holds the received object in the first transfer gripping area and transports the received object via a first drive to the second transfer component, wherein the second transfer component receives the object from the first transfer component, the second transfer component holds the received object in the second transfer gripping area and transports the received object via a second drive to the removal module, wherein the distance the object travels between the first transfer gripping area and the removal gripping area is greater than the length of the object in transport direction, and wherein the distance the object travels between the transfer gripping area and the second transfer gripping area is greater than the length of the object in transport direction.
 19. The sorting machine as claimed in claim 18, wherein a change of a first speed produced by the first drive is independent of a change of a second speed produced by the second drive.
 20. A method for the transport of a flat object in a transport direction, comprising: holding the object by a feeder module in a feeder gripping area; transporting the object from the feeder module to a first transfer component of a transfer module; holding the object by a first transfer gripping area of the first transfer component; transporting the object via a first drive from the first transfer component to a second transfer component of a transfer module; holding the object by a second transfer gripping area of the second transfer component; and transporting the object via a second drive from the second transfer component to the removal module, wherein a distance the object travels between the first transfer gripping area and the removal gripping area is greater than the length of the object in transport direction, and wherein a distance the object travels between the feeder gripping area is greater than the length of the object in transport direction.
 21. The method as claimed in claim 20, wherein a distance the object travels between the first transfer gripping area and the second transfer gripping area is smaller than the length of the object in transport direction.
 22. The method as claimed in claim 20, wherein a distance the object between the feeder gripping area and the first transfer gripping area is smaller than the length of the object in transport direction, and wherein a distance the object a distance the object travels between the second transfer gripping area and the removal gripping area is smaller than the length of the object in transport direction.
 23. The method as claimed in claim 20, wherein a change of a first speed produced by the first drive is independent of a change of a second speed produced by the second drive. 